Technical Field
The present disclosure relates to the field of ranging based on a time of flight calculation, and in particular to a read-out circuit of a ranging device.
Description of the Related Art
SPAD (single-photon avalanche diode) arrays can be used for a variety of applications, including for ranging, for Z or 3D gesture recognition and for 3D imaging. A device for such applications generally comprises a light source for transmitting an optical pulse into the image scene. The light reflected back from any object in the image scene is detected by the SPAD array, and used to determine the time of flight of the optical pulse. The distance from the object to the device can then be deduced based on this time of flight.
The detection by the SPAD array of the returning optical pulse is based on event detection in the cells of the SPAD array. In particular, each cell will provide an output pulse when a photon is detected, and by monitoring the events, the arrival time of the return pulse can be estimated.
A difficulty in such an event-driven system is that under very high ambient light and/or with a very reflective and/or close target, there may be a high number of events to be captured and processed in a short time frame, leading to congestion. Indeed, it would be inefficient and demanding on processing resources to perform range estimation based on the output of each SPAD cell. Therefore, the output of multiple SPADs are combined and processed as one signal. However, such a solution is limited by the devices used to combine the SPAD outputs, as these devices tend to become overloaded, leading to measurement inaccuracy.